The present disclosure relates to processes for coalescing toner particles made using emulsion/aggregation (E/A) processes, and incorporating continuous ramp and coalescence processes. These processes can be used to produce toner compositions.
Toner compositions are used with electrostatographic, electrophotographic or xerographic print or copy devices. In such devices, an imaging member or plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation, for example light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving substrate such as paper.
Emulsion aggregation (EA) toners are used in forming print and/or xerographic images. Emulsion aggregation techniques typically involve the formation of an emulsion latex of resin particles that have a small size of from, for example, about 5 to about 500 nanometers in diameter. Batch processes for producing resins may be subjected to bulk polycondensation polymerization in a batch reactor at an elevated temperature. The resulting resin in then cooled, crushed, and milled prior to being dissolved into a solvent. The dissolved resin is then subjected to a phase inversion process where the polyester resin is dispersed in an aqueous phase to prepare polyester latexes. The solvent is then removed from the aqueous phase by a distillation method. A colorant dispersion, for example of a pigment dispersed in water, optionally with additional resin, may be separately formed. The colorant dispersion may be added to the emulsion latex mixture, and an aggregating agent or complexing agent may then be added and/or aggregation may otherwise be initiated to form aggregated toner particles. The aggregated toner particles may be heated to enable coalescence/fusing, thereby achieving aggregated, fused toner particles.
Exemplary emulsion aggregation toners include acrylate-based toners, such as those based on styrene acrylate toner particles as illustrated in, for example, U.S. Pat. No. 6,120,967, the disclosure of which is totally incorporated herein by reference.
In conventional EA processes, batch processes may be used for preparing toners. Batch processes feature long processing times and consume a great deal of energy. The ramp/coalescence process is particularly time and energy intensive, as the entire batch is ramped to the desired coalescence temperature and maintained at that temperature for coalescence to occur. For example, in large-scale production of EA toner, increasing the temperature of toner to the desired coalescence temperature and carrying out the coalescence step may take upwards of 10 hours.
Additionally, in a batch process, high jacket temperatures and low fluid velocity at the walls under stirring can lead to fouling of the reactor walls. This necessitates additional down-time in the production cycle to allow for cleaning in order to restore the heat transfer from the jacket to the fluid in the vessel. This additional down-time further increases the total amount of time for running an extended production cycle to allow for cleaning after a set number of batches.
It would be desirable to provide coalescence processes that allow for the preparation of toner in a manner that is more efficient, takes less time, results in a consistent toner product, and possibly reduces energy consumption.